1. Field of the Invention
The present invention is generally in the field of communication methods and systems. More specifically, the present invention is in the field of network communication methods and systems.
2. Background Art
Universal Serial Bus (“USB”) ports provide convenient locations and an efficient power solution to charge portable devices using a widely adaptable USB cable and a personal computer, hub or USB charger. Portable devices, however, must accommodate the fact that a personal computer or hub draws a different amount of current than a USB charger. Consequently, a portable device must distinguish between different types of charging ports, including a Dedicated Charging Port (“DCC”)—a charging port corresponding to a USB charger, and a Charging Downstream Port (“CDP”)—a charging port corresponding to a personal computer or hub. A more detailed description of the general standards for charging portable devices using USB technology may be found in the USB Battery Charging Specification, Revision 1.1, published by USB Implementers Forum, Inc. (www.usb.org) on Apr. 15, 2009 (the “BC Spec”), which is hereby incorporated by reference in its entirety.
Conventional schemes to distinguish between CDP and DCP have a number of shortcomings. For example, as explained below, the detection process used in conventional schemes cause personal computers or hubs (using CD) to begin communication with the portable device, although the portable device merely intends to determine the type of charging port.
FIG. 1 shows dedicated charging port (“DCP”) circuit 100 adapted to connect to a portable device. Supply voltage pin 106 provides a positive supply voltage of a value VBUS to DCP circuit 100, and ground pin 112 provides a ground voltage to DCP circuit 100. Positive data line 108 and negative data line 110 are connected through a resistor or resistive network such as resistor 104 with value RCHG DAT. As described in the BC Spec, operates at 5.25 Volts (V) and VBUS RCHG DAT has a value or 200 ohms. DCP circuit 100 may provide a portable device with up to 1.8 Amperes (A) of current at 5.25 V through supply voltage pin 106. Since DCP circuit 100 shorts positive data line 108 and negative data line 110 with resistor 104, DCP circuit 100 does not transfer data to or from a connected portable device. For example, a binary signal that has a step transition between a logical LOW value of below 0.8 V and a logical HIGH value of above 2.0 V on positive data line 108 merely returns to negative data line 110 through resistor. Consequently, DCP circuit 100 can charge a portable device but is incapable of processing logical data for a portable device or supporting data communications between a host and a device.
FIG. 2 illustrates charging downstream port (“CDP”) circuit 200. CDP circuit 200 includes supply voltage pin 206, ground pin 212, positive data line 208 and negative data line 210. These pins are similar to respective pins illustrated in DCP circuit 100 of FIG. 1. Internally, CDP circuit 200 includes positive switch 236, positive pull-down resistor 220, comparator 228, positive data line current sink 230, negative data line voltage source 224, negative switch 226, negative pull-down resistor 222, and AND gate 240. Portable detect signal 238 comes from AND gate 240 into physical layer 204. Portable detect signal 238 may be configured to correspond to digital logic values, including for example, a value of 0 to 0.8 V corresponding to a logical LOW signal and a value of above 2.0 V corresponding to a logical HIGH signal. As shown in FIG. 2, CDP circuit 200 includes comparator 228, as well as leakage resistors 216 and leakage voltages 218. Positive data line current sink 230 is configured to draw between 50 and 150 microamperes (μA) of current. Negative data line voltage source 224 is configured to provide between 0.5 and 0.7 V. Data detect voltage 232 provides a voltage between 0.25 and 0.4 V.
CDP circuit 200 in FIG. 2 is capable of supporting data communication between a host coupled thereto and a device. More specifically, CDP circuit 200 can receive differential signals corresponding to logical LOW or logical HIGH voltages in differential form across positive data line 208 and negative data line 210. These differential voltages may correspond to packetized information, including for example, control instructions or data, which are used for communicate between the portable device and a host coupled to CDP circuit 200.
One means of communication via a CDP circuit 200 is by driving a voltage equal to negative data line voltage source 224 onto negative data line 210. When CDP circuit 200 receives a voltage on positive data line 208 that is greater than data detect voltage 232 and is less than the logic threshold of CDP circuit 200 (namely below the logical LOW threshold voltage value of 0.8 V), portable detect signal 238 is asserted. CDP circuit 200 actively responds to this signal by switching negative switch 226 and driving the voltage at negative data line voltage source 224 onto negative data line 210, actively transmitting that value back to the portable device. For example, if a voltage on positive data line 210 lies between 0.4 V (the maximum value of data detect voltage source 224) and 0.8 V (the minimum value of the logic threshold voltage), a voltage of between 0.5 V and 0.7 V corresponding to negative data line voltage source 224 will be applied to negative data line 210 and transmitted back to the portable device.
Turning to FIG. 3, FIG. 3 illustrates conventional portable device circuit 300 adapted to connect to either a DCP or a CDP. Conventional portable device circuit 300 comprises pins to interface to a DCP or a CDP, including supply voltage pin 306 to draw charge, ground pin 312, positive data line 308, negative data line 310 and ID pin 314. Positive data line 308 and negative data line 310 allow conventional portable device circuit 300 to distinguish between a DCP or a CDP using logical signals in differential form.
Internally, conventional portable device circuit 300 includes voltage switch 352, current switch 354, comparator switch 356, pull-down switch 368, and pull down resistor 370. Conventional portable device circuit 300 further includes positive data line voltage source 348, data connect detect current source 350, negative data line current sink 358, data detect voltage 360 and AND gate 364. Comparator 362 is capable of comparing data detect voltage 360 with a voltage on negative data line 310. Charger detect signal 366 comes into physical layer 342 through AND gate 364. Physical layer 342 includes leakage resistors 344 with leakage voltages 346. Negative data line current sink 358 is configured to draw between 50 and 150 microamperes (μA) of current. Positive data line voltage source 348 is configured to provide between 0.5 and 0.7 V.
During a start-up sequence, conventional portable device circuit 300 is required to detect a charging port and classify the detected charging port as a DCP or a CDP to determine how much current it can draw from the charging port. Conventional portable device circuit 300 begins operation in low bandwidth of full bandwidth mode. Conventional portable device circuit 300 then closes voltage switch 352, current switch 354 and comparator switch 356 to raise the voltage on positive data line 308 to positive data line source voltage 348, that is to a logical HIGH. After a positive voltage source on time of about 40 milliseconds (ms), conventional portable device circuit 300 then checks the voltage at negative data line 310. If the voltage at negative data line 310 is above data detect voltage 360 but below the logic threshold of conventional portable device circuit 300, conventional portable device circuit 300 has detected that a charging port is attached and is allowed to draw a specified portable device current from the charging port.
To classify the attached charging port as a DCP or a CDP, conventional portable device circuit 300 asserts a logical HIGH value (that is a value exceeding the circuit's logical threshold voltage of 2.0 V) onto positive data line 308. If the attached charging port is a DCP, the voltage on negative data line 310 will also go to a logical HIGH value, because a DCP shorts positive data line 308 and negative data line 310 through an internal resistor (shown in FIG. 1). Thus, despite the presence of the internal resistor, the voltage at negative data line will reach a logical HIGH value and allow conventional portable device circuit 300 to determine that a DCP is connected. In such a case, conventional portable device circuit 300 and may attempt to draw a current of up to 1.8 A.
On the other hand, if the attached port is a CDP, the voltage on positive data line 308 will cause a communication with the portable device. Consistent with FIG. 3, the voltage on positive data line 308 will correspond to a logical HIGH. The CDP will recognize a voltage exceeding the logical threshold value, and will not drive that voltage to negative data line 310 thereby communicating a voltage value of a logical LOW back to conventional portable device circuit 300. Thus, if a CDP is attached, the voltage at negative data line 310 will remain at a logical LOW value of below 0.8 V despite the fact that the voltage at positive data line 308 was raised to a logical HIGH value. In such a case, conventional portable device circuit 300 will know that a CDP is attached. Conventional portable device circuit 300 will draw a current of 1.5 A at low or full bandwidths. If a CDP is attached, the USB system may later enter high bandwidth mode and draw a current 900 mA in that mode. Requiring the CDP to process the logical transitions outlined above and requiring the CDP to communicate a voltage value of a logical LOW back to conventional portable device circuit 300 undermines the robustness of the USB system, as it causes the host coupled to the CDP to attempt data communications with the portable device that is merely trying to determine the type of charging port.
Accordingly, there is a need to overcome the drawbacks and deficiencies in the art by providing methods and systems for a portable USB-compatible devices for distinguishing between charging ports, which enhance interoperability of the portable device with the charging port, while remaining compatible with existing USB technology.